This invention relates in general to squaraines, and more specifically, to squaraine compositions of matter, process for preparing the squaraine compositions of matter, articles containing the squaraine compositions of matter and methods of using the articles containing the squaraine compositions of matter.
Squaraine compositions are useful for incorporation into photoresponsive devices to extend the response capability of such devices to visible light as well as infrared illumination. These photoresponsive devices can therefore be utilized, for example, in conventional electrophotographic copiers as well as in laser printers. These photoresponsive devices may comprise single or multilayered members containing photoconductive materials comprising squaraine compositions in a photogenerating layer, between a photogenerating layer and a hole transport layer, or between a photogenerating layer and a supporting substrate.
In one process for preparing squaraine compositions a dialkyl squarate can be reacted with an aniline compound. Thus, for example, in copending application Ser. No. 557,796, entitled Preparations of Squaraines Compositions, filed in the name of Kock Yee-Law concurrently herewith, a dialkyl squarate and an N,N-dialkyl aniline, in the presence of an acid catalyst, are reacted at a temperature of from about 80.degree. C. to 160.degree. C. Solvents, such as aliphatic alcohols, including methanol, ethanol, propanol, butanol, especially water saturated 1-butanol, amyl alcohol, are selected for the purpose of forming a solution of the squarate and the acid.
In still another process for preparing squaraine compositions squaric acid is reacted with a tertiary aromatic amine compound. Thus, for example, in copending application Ser. No. 557,801, entitled Process For Synthesizing Squaraine Compositions, filed in the name of John F. Yanus concurrently herewith, squaric acid, a long chain primary alcohol having a boiling point between about 130.degree. C. and about 210.degree. C. and a tertiary aromatic amine are heated in vacuo below the boiling points of the primary alcohol and the tertiary amine to form a squaraine composition.
Photoconductive imaging members containing certain squaraine compositions, including amine derivatives of squaric acid, are known. Also known are layered photoresponsive devices containing photogenerating layers and transport layers, as described, for example in U.S. Pat. No. 4,123,27, U.S. Pat. No. 4,353,971, U.S. Pat. No. 3,838,095, and U.S. Pat. No. 3,824,099. Examples of photogenerating layer compositions disclosed in U.S. Pat. No. 4,123,270 include 2,4-bis-(2-methyl-4-dimethylamino-phenyl)-1,3-cyclobutadiene-diylium-1,3-d iolate, 2,4-bis-(2-hydroxy-4-dimethylamino-phenyl)-1,3-cyclobutadiene-diylium-1,3- diolate, and 2,4-bis-(p-dimethylamino-phenyl)-1,3-cyclobutadiene-diylium-1,3-diolate.
Although all the amine derivatives of squaraic acid described in U.S. Pat. No. 4,123,270, U.S. Pat. No. 4,353,971, U.S. Pat. No. 3,838,095, and U.S. Pat. No. 3,824,099 are symmetrical, a specific unsymmetrical, fused ring, nonamine derivative of squaric acid having hydroxy groups on a fused ring is disclosed in U.S. Pat. No. 4,353,971 and U.S. Pat. No. 3,824,099.
In Loutfy et al, "Photocoductivity of Organic Particle Dispersions: Squarine Dyes", Photographic Science and Engineering, Vol. 27, No. 1, January/February, 1982, pp 5-9, a structural formula of an amine derivative of squaric acid is illustrated on page 8 that is obviously a misprint in view of the text of the article.
The formation and development of electrostatic latent images on the imaging surface of photoconductive members by electrostatic means is well known. Generally, the method involves the formation of an electrostatic latent image on the surface of an electrophotographic plate, referred to in the art as a photoreceptor. This photoreceptor usually comprises a conductive substrate and one or more layers of photoconductive insulating material. A thin barrier layer may be interposed between the substrate and the photoconductive layer in order to prevent undesirable charge injection.
Many different photoconductive members are known including, for example, a homogeneous layer of a single material such as vitreous selenium, or a composite layered device containing a dispersion of a photoconductive composition. An example of one type of composite photoconductive member is described, for example, in U.S. Pat. No. 3,121,006. The composite photoconductive member of this patent comprises finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The photoconductive inorganic compound usually comprises zinc oxide particles uniformly dispersed in an electrically insulating organic resin binder coated on a paper backing. The binder materials disclosed in this patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. The photoconductive particles must therefore be in substantially contiguous particle to particle contact throughout the layer to permit the charge dissipation required for a cyclic operation. The uniform dispersion of photoconductive particles requires a relatively high volume concentration of photoconductor material, usually about 50 percent by volume, in order to obtain sufficient photoconductor particle to particle contact for rapid discharge. This high photoconductive particle loading can adversely affect the physical continuity of the resinous binder thereby significantly degrading the mechanical properties thereof. Specific binder materials disclosed in this patent include, for example, polycarbonate resins, polyester resins, polyamide resins, and the like.
Also known are photoreceptor materials comprising inorganic or organic materials wherein the charge carrier generating, and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material. However, the art of xerography continues to advance and more stringent demands need to be met by the electrostatographic imaging apparatus in order to improve performance, and to obtain higher quality images. Also desired are layered photoresponsive devices which are responsive to visible light and/or infrared illumination for certain laser printing applications.
Other layered photoresponsive devices including those comprising separate generating and transport layers are described, for example, in U.S. Pat. No. 4,265,990. Overcoated photoresponsive materials containing a hole injecting layer, overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and an outer coating of an insulating organic resin are described, for example, in U.S. Pat. No. 4,251,612. Photogenerating layers disclosed in these patents include, for example, trigonal selenium and phthalocyanines and transport layers including certain diamines. The disclosures of U.S. Pat. Nos. 4,265,990 and 4,251,612 are incorporated herein by reference in their entirety.
There is also disclosed in Belgium Pat. No. 763,540, an electrophotographic member having at least two electrically operative layers, the first layer comprising a photoconductive layer which is capable of photogenerating charge carriers and injecting the carriers into a continuous active layer containing an organic transporting material which is substantially non-absorbing in the spectral region of intended use, but which is active in that it allows the injection of photogenerated holes from the photoconductive layer and allows these holes to be transported through the active layer. Additionally, there is disclosed in U.S. Pat. No. 3,041,116, a photoconductive material containing a transparent plastic material overcoated on a layer of vitreous selenium contained on a substrate.
While photoresponsive devices containing the above-described known squaraine materials are suitable for their intended purposes, there continues to be a need for the development of novel squaraine materals, improved processes for preparing the squaraine materials, and improved devices utilyzing the novel squaraine materials.